CVE-2026-6686

MEDIUM LAB

FatFs Use of Uninitialized Clusters After Seek Past EOF

Title source: cna
STIX 2.1

Description

FatFs R0.16 and earlier contains an uninitialized cluster exposure when f_lseek() extends files beyond EOF without zero-filling newly allocated clusters. This maps to CWE-908 (Use of Uninitialized Resource). Estimated CVSS v3.1 vector: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N (4.6, Medium). The estimated CISA SSVC vectors are Exploitation: PoC, Technical Impact: Partial.

References (4)

Core 4
Core References
Third Party Advisory third-party-advisory
https://www.runzero.com/blog/fatfs-bugs/

Scores

CVSS v3 4.6
EPSS 0.0038
EPSS Percentile 30.5%
Attack Vector PHYSICAL
CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

CISA SSVC

Vulnrichment
Exploitation poc
Automatable no
Technical Impact partial

Lab Environment

COMMUNITY
Community Lab
docker pull espressif/idf:v5.3.2

Details

CWE
CWE-908
Status published
Products (2)
ChaN/FatFs < R0.16
elm-chan/fatfs < r0.16
Published Jul 01, 2026
Tracked Since Jul 01, 2026